ESXi 40 does ship with the ability to run SSH, but this is disabled by default (and is not supported). If you just need to access the console of ESXi, then you only need to perform steps 1 - 3.

1) At the console of the ESXi host, press ALT-F1 to access the console window.
2) Enter unsupported in the console and then press Enter. You will not see the text you type in.
3) If you typed in unsupported correctly, you will see the Tech Support Mode warning and a password prompt. Enter the password for the root login.
4) You should then see the prompt of ~ #. Edit the file inetd.conf (enter the command vi /etc/inetd.conf).
5) Find the lines that begins with #ssh and remove the #. Then save the file. If you're new to using vi, then move the cursor down to #ssh line and then press the Insert key. Move the cursor over one space and then hit backspace to delete the #. Then press ESC and type in :wq to save the file and exit vi. If you make a mistake, you can press the ESC key and then type it :q! to quit vi without saving the file. Note: there are two lines for SSH with ESXi 4.0 now - one for regular IP and the other for IPv6. You should the line appropriate to the protocol you'll use to access your host.
6) Once you've closed the vi editor, you can either restart the host or restart the inetd process. To restart inetd run ps | grep inetd to determine the process ID for the inetd process. The output of the command will be something like 1299 1299 busybox inetd, and the process ID is 1299. Then run kill -HUP <process_id> (kill -HUP 1299 in this example) and you'll then be able to access the host via SSH.

Tip - with some applications like WinSCP, the default encryption cipher used is AES. If you change that to Blowfish you will likely see significantly faster transfers.

Changing the port for SSH

To change the port for SSH, edit the file /etc/services and change the SSH port listed in the file. Save the file and repeat step 6 above.

Enable Telnet

The steps are the same as with SSH, but you'll remove the # from the 2 telnet entries in /etc/inetd.conf. Enabling telnet is not recommended if security is a concern.

You can also download an oem.tgz file which will enable SSH (and FTP). Copy the file to a datastore with the VI client and then to bootbank with the command cp /vmfs/volumes/<datastore>/oem.tgz /bootbank/oem.tgz and then reboot.

Enable SSH access for a non-root account

Use the following process to enable SSH access for a non-root account
1) Access SSH or the console with a root account.
2) Create a new account with the command useradd <account_name> -M -d/ . This will set the home directory to / instead of requiring a /home directory.
3) Use the command passwd <account_name> to set the password for your new login.
4) Edit the passwd file with vi /etc/passwd. For the entry for your new account, change the /bin/sh part to /bin/ash. Save the file and exit. See the example for the test1 user below.

If you have created non-root accounts for SSH access you can also disable root access via SSH. Edit the /etc/inetd.conf file using the initial process on this page and add the option -w after the -i option. The line in inetd.conf will appear similar to the below.

One you have made the change, save the file and run the kill -HUP command to restart the inetd process. You will now be able to login with a non-root account, but will get access denied if you use a root account. Once you have established a SSH session with your non-root account you can issue the command su - to switch to the root account.